Help with physics??

Question

A constant net force of 410 N is applied upward to a stone that weighs 36 N. The upward force is applied through a distance of 2.0 m, and the stone is then released. To what height, from the point of release, will the stone rise? Assume that air resistance is negligible.

_______m

Answer 1

1st, convert weight to mass:

36N/(9.8m/s) = ?kg

2nd, find acceleration of stone (due to applied force), accounting for the acceleration due to gravity in the opposite direction.

F = ma + mg --> a = F/m - g

3rd, find velocity of stone after being accelerated for 2m.

[v(f)]^2 = [v(i)]^2 + 2 * a * d

Use v(i)=0, as it assumedly starts from rest.

Thus, v(f) = sqrt(2 * a * d)

4th, find distance the stone rises from the 2m point.

Again, use [v(f)]^2 = [v(i)]^2 + 2 * a * d

This time, however, v(f)=0, as that occurs at max altitude; and v(i) will be equal to the v(f) obtained in the 3rd step.

Also, the acceleration is now due to gravity alone, as the stone has become a projectile.

The equation then becomes d = ([v(i)]^2) / (2 * g).

The problem is basically broken into two parts

1 - what happens during the first 2m, as the force is applied; steps 1-3.

2 - what happens after 2m, while the stone is a projectile; step 4.

Draw a picture of the 2 parts of the problem; and keep track of the - signs.